1. Field of the Invention
This invention relates to a process for preparing high quality, camera speed direct positive images using a novel photographic imaging system which employs low coating weight silver halide elements. These elements can be used to advantage in place of any of the conventional direct positive elements. Because of the unique advantage of this novel system, the elements of this invention are faster and have better image quality than the prior art.
2. Description of the Prior Art
The use of non-photosensitive layers and materials in conjunction with photosensitive elements is well-known. Colorants, for example, are used to enhance or tone the image formed in the photosensitive layers. Colorant layers are also used as anti-halation layers for the photosensitive layer and the like. Schneider in U.S. Pat. No. 1,971,430 teaches the use of colloidal silver in a binding agent designed for use as an anti-halation layer for a silver halide element. The use of colloidal silver in color film elements is also known from Mannes et al. U.S. Pat. No. 2,143,787 and others. Shuman in Defensive Publication T900,010, published 7/18/72 describes how blue colloidal silver with a very small particle size can be changed to the yellow form by contacting with halide ions. According to T900,010 this process may be accomplished imagewise by contacting the blue colloidal silver layer with an exposed and developed silver halide image. Thus, the image results in the change of color from blue to yellow in the area corresponding to the developed silver halide image. This prior art does not teach, however, imagewise chemically bleaching a colorant layer in conjunction with a photosensitive developable or developed silver halide layer to produce camera speed, direct positive high quality images therefrom. British Pat. No. 1,380,259 relates to high density silver images formed as a sound track for a 3-color negative process and to a method for retaining this metallic silver duurig the dye bleaching process. Final image amplification is not taught nor is the concept of that patent related to the novel elements and process described herein. In yet another system, the applicant has taught in U.S. Pat. No. 3,413,122 that high density images can be formed using low covering power high sensitivity silver halide layers in conjunction with high covering power low sensitivity silver halide layers. That patent does not teach, however, imagewise chemically bleaching a colorant layer in conjunction with a photosensitive layer to produce high speed, high quality, direct positive images therefrom.